Plasma arc torches are widely used in the cutting and marking of materials. A plasma arc torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). The torch produces a plasma arc, i.e., a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air). During operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or by means of any of a variety of starting methods.
In many prior art plasma arc torches, coolant travels along a circuitous path within the torch (e.g., forward to the nozzle, then back to the torch head, then forward to the shield, then back to the torch head), requiring a significant driving force to propel the coolant within the torch. An example of such a prior art torch is shown and described in U.S. Pat. No. 8,389,887, entitled “Apparatus and method for a liquid cooled shield for improved piercing performance.” In this arrangement, coolant flows from a source through the plasma arc torch to a surface of the shield and back through the plasma arc torch, requiring multiple trips for the coolant to contact both the shield and the nozzle. Still some other prior art torches have substantial deadspots in the coolant flow and/or unidirectional coolant flow which does not provide even cooling to the nozzle, shield, and other consumables in the torch tip. What is needed is a configuration in which the coolant is routed directly to the consumables, such that a minimal driving force is required to move coolant through the plasma arc torch in a substantially uniform and symmetrical manner.